Adhesive tape comes in many varieties; for example, single-sided or double-sided tape, typically wound into a roll. Double-sided adhesive tape (also termed “adhesive transfer tapes”) has adhesive properties on both sides, generally covered by a liner to protect the adhesive, which is removed prior to when the adhesive layer is bonded to a substrate. In some embodiments, a double-sided release liner is used, wherein a first release layer is coated on a first major surface of a backing, and a second release layer is coated on a second major surface of the backing opposite the first major surface. Typically, the first and second release layers are designed to have different release properties to facilitate dispensing the tape in roll form. For example, the first release layer may bind somewhat more tightly to the adhesive layer than the second release layer in order to achieve a clean unwind of the roll.
Methods of producing double-sided adhesive tape can be relatively simple, and one method of production and the resulting structure is as follows. A layer of an adhesive composition is readied and extruded, or otherwise coated by some acceptable method, onto the first release layer of the release liner. For high performance adhesive tapes, the adhesive composition is often then crosslinked (e.g., chemically, by visible or ultraviolet light, or by electron beam radiation). Next, the double-sided release liner and adhesive construction is wound into a roll such that the adhesive layer is sandwiched between the first and second release layers.
Production of double-sided adhesive tape by this method is desirable, but significant problems are encountered when electron beam (“E-Beam”) radiation is used to crosslink the adhesive polymer. E-Beam radiation is advantageous as a method of crosslinking because it is effective to crosslink adhesive polymers that have high amounts of pigments or fillers, and/or adhesive films of greater thicknesses. In tape constructions with a single double-sided liner, it is typically necessary to perform the electron beam (E-Beam) exposure step with a major surface of the silicone release layer exposed (the exposed surface) to the ambient environment of the E-Beam processing chamber. If the exposed surface of the silicone release layer is exposed to E-Beam radiation (“E-Beam treated”) before winding into a roll, the release properties of the silicone release layer as adhered to the adhesive layer itself are typically altered in a deleterious fashion.
Moreover, in this configuration the adhesive bond between the adhesive layer and the release layer onto which it is subsequently wound tends to increase over time, leading to unpredictable product performance. This can create an undesirable situation in the final product wherein the adhesion of the adhesive layer to both release layers is comparable, resulting in what is known as “liner confusion”. In some cases, the release liner cannot even be removed. This is known as “liner blocking”. Even when the adhesive material is E-Beam treated directly (i.e., not through a release liner), the side of the silicone release layer opposite the adhesive material will typically be affected if the radiation penetrates through the liner.
One solution to this problem has been to manufacture the double-sided adhesive tape on a temporary liner, crosslink the adhesive with E-Beam radiation, and then replace the temporary release liner with another release liner before it is packaged into the final product. However, this solution is unacceptable because it adds to the complexity of the process, increases waste of the process, and adds the additional cost of another liner. Therefore, there is a need for a release liner that can be E-Beam treated while still maintaining essentially the same pre-E-Beam treated release characteristics so that it need not be replaced before the consumer can utilize the final product.